Fix for BUG#2083

"EE_ error codes (EE_DELETE, EE_WRITE) end up in the binlog, making slave stop".
The problem was that during execution of the command on the master, an error
can occur (for example, not space left on device, then mysqld waits and when
there is space it completes successfully: so finally it worked but the error
EE_WRITE remains in thd->net.last_errno and thd->net.last_error).
To know if finally the command succeeded, we test the 'error' variable in
every place, and if it shows no failure we reset thd->net.last_err* using
the function THD::clear_error() which is backported from 4.1.
A new test to see if now only real errors get to the binlog (note: the test
uses "rm").

Also a bit of memory free/alloc saving in log_event.cc (do not free the whole
mem_root after every query in the slave SQL thread: we can keep the initial
block of it; which will be freed when the thread terminates).


sql/log_event.cc:
  In the slave SQL thread, it's a waste to free the initial block of the mem_root
  after every query. We can instead keep it. It will be freed when the thread
  terminates (in THD::~THD()).
sql/sql_acl.cc:
  clear the error in thd->net.last_errno as there was no error
sql/sql_base.cc:
  clear the error in thd->net.last_errno as there was no error
sql/sql_class.h:
  Backport of THD::clear_error() from 4.1:
  clears the error in thd->net.last_errno
sql/sql_db.cc:
  clear the error in thd->net.last_errno as there was no error
sql/sql_delete.cc:
  clear the error in thd->net.last_errno as there was no error
sql/sql_insert.cc:
  clear the error in thd->net.last_errno as there was no error
sql/sql_parse.cc:
  clear the error in thd->net.last_errno as there was no error
sql/sql_rename.cc:
  clear the error in thd->net.last_errno as there was no error
sql/sql_table.cc:
  clear the error in thd->net.last_errno as there was no error
sql/sql_update.cc:
  clear the error in thd->net.last_errno as there was no error

sql/sql_rename.cc

@@ -82,6 +82,7 @@ bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list)
     mysql_update_log.write(thd,thd->query,thd->query_length);
     if (mysql_bin_log.is_open())
     {
+      thd->clear_error();
       Query_log_event qinfo(thd, thd->query, thd->query_length, 0);
       mysql_bin_log.write(&qinfo);
     }